// do nothing function // pure virtual function //abstract class
#include <iostream>
using namespace std;

class Person       // abstract class coz of pure virtual func - so no obj can be created of Person
{
    public:
        virtual void fun()=0; // pure virtual function
};

class Student: public Person
{
    public:
        void fun() {} // over-riding is compulsory for derived class
};

int main()
{
    // Person s1; // not possible
    Student s1;
    s1.fun();
}